IEEE 802.11 is a set of standards for implementing wireless local area networks (WLANs). Depending on which standard is employed, such as IEEE 802.11b, 802.11g, or 802.11n, IEEE 802.11 networks commonly operate in the 2.4, 3.6, and 5 GHz frequency bands. IEEE 802.11 divides the frequency bands into channels; for example, the 2.4000-2.4835 GHz band, utilized in IEEE 802.11b and 802.11g networks, is divided into 13 channels spaced 5 MHz apart, with channel 1 centered on 2.412 GHz and 13 on 2.472 GHz. In an 802.11b network, which utilizes 22 MHz channels, only three channels in the 2.4 GHz band do not overlap—channels 1, 6, and 11. In an 802.11g network, which utilizes 20 MHz channels, there are four non-overlapping channels: 1, 5, 9 and 13. IEEE 802.11 specifies two network modes, infrastructure mode and ad hoc mode. In the ad hoc mode, clients connected to the same WLAN communicate directly with other peers on the same WLAN to form a peer-to-peer network. In the infrastructure mode, one or more network infrastructure devices, such as wireless access points or wireless routers, are responsible for broadcasting the network; clients then connect to the network infrastructure devices to form a network and the clients communicate with each other through the network infrastructure devices.
IEEE 802.11 standards define frame types for data transmission, management, and connection control of connections in the WLAN. A beacon frame is a management frame containing information about the WLAN. Beacon frames are transmitted periodically to announce the presence of a WLAN, transmitted periodically to announce the presence of a WLAN. Beacon frames in 802.11 networks contain information about the sender and the recipient of the beacon frame along with a variety of network information including the beacon interval, a timestamp, a service set identifier (SSID) identifying the network, a description of the data rates available on the network, information concerning the signaling methods utilized in the network, the capability information of the network, and in some beacon frames, a traffic indication map. In ad hoc networks, each network client, also known as a peer, generates beacon frames. The time between beacon frame transmissions is known as the beacon interval. In an ad hoc network, one peer configures itself to send the beacon frame. After receiving a beacon frame, the other peers wait for the beacon interval and then broadcast a beacon frame if no other station has done so within the beacon interval plus a random amount of additional time, ensuring that at least one peer will send a beacon frame and that the beacon frame transmission responsibilities are shared amongst the peers in a WLAN. In an infrastructure network, the network infrastructure devices are responsible for transmitting beacon frames. In the event that the network infrastructure devices are unavailable, the network is inaccessible to network clients.